Guide To Hearing

Joan McKechnie

BSc Hons Audiology & Speech Pathology

My name is Joan, your audiologist here at HearingDirect.com. The following is a guide to hearing that covers many of the questions I receive on a regular basis about all things hearing. I am constantly adding to the information featured here based on your feedback and questions. If you would like to see more information on a particular subject or have a subject you would like to see introduced; I would be delighted to hear from you - click here to submit a question/subject or feel free to give me a call on 1-800-805-694.

"Hearing is a precious gift which helps us make sense of the world around us. Scientists tell us that our ears pick up air waves and translate them into sounds in our brain but hearing is so much more than that; chatting with friends, listening to our children, talking through problems or relaxing to music. Sounds provide information and evoke thoughts and feelings that give meaning to our lives."

What is sound?

Put simply, “Sound” is waves or vibrations of air. A healthy ear is able to pick up vibrations that are measured in a basic unit of frequency known as Hertz or Hz. The ear converts vibrations into electrical signals sent to the brain, where they are translated into meaningful information such as speech and music.

Our brain works out what type of sound it is according to the volume and the pitch of the vibrations. The volume of sound is measured in decibels or dB SPL. The greater the volume the further the sound travels and the louder it sounds.

The rate at which a sound vibrates is called its frequency and the higher the frequency the higher-pitched the sound, such as a piccolo or birdsong. Low-pitched sounds could be the rumble of distant thunder. Frequency is physical measurement and pitch is a measure of how we perceive frequency.

Loudness varies from person to person and as such it would help to mention here how loudness is described: inaudible, very soft, soft, moderate, loud, very loud or too loud. For the same volume of sound, people might rate them differently. For example, one might rate rock music as loud and another might rate it as too loud.

The characteristics of different sounds vary widely. Simple sounds such as pure tones contain only one frequency. However, most everyday sounds are complex sounds consisting of many frequencies. Speech, for example, consists of vibrations at different volumes and numerous frequencies and most are between 250 and 8000Hz.

How do we hear?

Sound travels in waves of pressure through water, gases (like air) and other matter. It is the means of auditory communication but how do we make sense of what we hear? The human ear is designed to be a receiver of sounds but also plays a major role in balance and body position.

Our ears are divided into three parts – the outer ear, the middle ear and the inner ear. Sound waves travel through each part of the ear to the brain where they are analyzed and interpreted into meaning. The best way to describe how our ears work is to describe the pathway sound takes through each part:

1) The outer ear

The outer ear includes the pinna (also called the auricle), the ear canal and the eardrum (also called the tympanic membrane). The pinna is the external part of the ear made of cartilage, tissue and skin. It collects and directs sounds into the ear canal and protects the ear canal. The ear canal is a tube that directs sounds onto the eardrum.

2) The middle ear

The middle ear is an air-filled chamber connected to the nasal and throat passages by the Eustachian tube which equalizes air pressure on both sides of the ear drum. Usually closed, the Eustachian tube opens naturally when you swallow or yawn. Sound reaching the eardrum causes it to vibrate, transmitting that sound to the three smallest bones in the body. These bones or ‘ossicles’ are commonly referred to as the hammer (or Malleus), the anvil (or Incus) and the stirrup (or Stapes) that connect the eardrum to the inner ear. These tiny ossicles amplify the vibrations and direct the waves of sound into the inner ear.

3) The inner ear

The inner ear is filled with a fluid and consists of the spiral shaped Cochlea, named from the ancient word for the shell of a snail. The passageways of the cochlea are lined with over 15,000 microscopic haircells (called inner and outer hair cells) that convert sound vibrations from the ossicles into nerve pulses which are then sent to the brain. The auditory nerve contains thousands of nerve fibres that help our brains interpret these pulses into meaning. The inner ear also contains our ‘vestibular system’ which is critical for maintaining balance and body position.

What can go wrong?

Types and causes of hearing loss

Whilst there are many reasons for hearing loss, the condition itself falls into two main categories: Conductive and Sensorineural. Hearing loss can also be attributed to a combination of both types – a mixed hearing loss.

Conductive hearing loss is caused by any obstruction that prevents sound waves from reaching the inner ear. Some of the causes of conductive hearing loss can include:

An accumulation of earwax

A collection of fluid in the middle ear (for example, “glue ear” in children)

Abnormal bone growth in the middle ear (otosclerosis)

Middle ear infections (otitis media)

Perforation of the eardrum

Sensorineural hearing loss refers to problems in the cochlea or the auditory nerve.

Most are due to deterioration of the tiny inner or outer hair cells. This accounts for 90% of permanent hearing losses and although it may be a natural part of aging other causes can include:

Traumatic exposure to noise

Head injury

Viral infections of the inner ear and/or auditory nerve such as Mumps

Certain medical treatments such as chemo- and radiation therapy

Genetic predisposition

Sensorineural hearing losses cannot currently be corrected medically

It is quite possible for a conductive hearing loss to occur together with a sensorineural hearing loss. When this occurs, the hearing loss is referred to as a mixed hearing loss.

Noise-induced hearing loss

A common cause of hearing loss is caused through prolonged exposure to harmful sound (noise) or a sudden brief but intense noise like an explosion to the ear. The nature of noise-induced hearing loss is sensorineural, and at present, can only be helped and not cured. Most people with hearing loss caused by noise exposure could have avoided it happening. Excessive noise exposure can happen unknowingly at home in the form of music on an MP3 player, for example, or as a by-product of the workplace environment. The human ear collects sound at frequencies of between 20Hz and 20000Hz. Our ears are most sensitive at the 2000-5000Hz range which is important for speech and where continuous exposure to noise causes the most damage.

One way we can prevent hearing loss is by staying in environments with safe sound limits. Many of us can routinely be exposed to the harmful effects of sound every day. Our ears can put up with very high levels of noise for very short periods of time but the louder the noise, the less time we can spend listening to it before damage is done. Most of us can sustain noises of 90 decibels for up to eight hours without permanent damage, for example, but at 100 decibels the maximum time is only two hours. The figure below shows some typical values for noise sources:

These are the guidelines as to the thresholds that must not be exceeded in the working environment published by the Health and Safety Executive:

Daily or weekly exposure - 87dB

Peak sound pressure - 140dB

Earplugs are a very effective way of protecting hearing. They are available in a variety of materials including foam, wax, rubber and silicone. Musicians, for example, wear custom-fitted earplugs that do not distort music or impact performance. Foam earplugs are the cheapest and can reduce sounds entering the inner ear by up to 35dB.

Occupations particularly at risk of hearing loss due to exposure to noise include fire fighters, police officers, factory workers, farmers, construction workers, military personnel, heavy industry workers, musicians, and entertainment industry professionals. It is important to wear hearing protection properly and all the time when involved in noisy work or located in hearing protection areas.

What does a hearing assessment involve?

Hearing tests are quick and relatively simple for the person being tested. Results are instant, and you will know immediately if you do have a hearing problem and what steps to take. To many the results of a test, whatever they are, come as a huge relief. Once they have sought that initial help they find the subsequent process straightforward and altogether life changing.

Your hearing healthcare professional will usually begin by asking you questions about the health of your ears and general health and your lifestyle. By asking these questions they can determine the possible damage that may have been caused to your ears from such things as illness, age, your job, your hobbies etc.

Ear examination

A physical examination of your ears is performed to eliminate any medical problems such as infections or blockages such as wax. Otoscopy is an examination that involves looking into the ear canal with the cone of an otoscope. Inspection of the eardrum can also provide information about what is happening within the middle ear.

What happens during a hearing test?

Amongst all the tests that can be performed on your hearing, pure tone audiometry is the most common. This evaluates the sensitivity of your sense of hearing at different frequencies. A set of headphones is worn over the ears or foam earphones placed in the ear canal; and you may be required to sit in a sound-proof test room. The headphones are then connected to the audiometer.

This piece of specialized equipment produces tones at specific frequencies and levels to each ear independently. The patient will communicate that they have heard the tone by either raising their hand or pressing a button. As the test progresses, the hearing professional will plot results on an audiogram where the frequency is on the horizontal axis and the loudness is on the vertical axis. Once each frequency has been tested and plotted, the points are joined by a line so that you can easily see your results and compare them to what is considered to be within normal limits. These results are your ‘thresholds’. Normal hearing at any frequency is a threshold of 20dB or quieter, and with worsening hearing that number increases.

What do the results of an audiogram mean?

At the end of a hearing test you may be told that you have normal hearing or a mild, moderate, severe or profound loss of hearing. The image below shows an example of an audiogram.

Hearing loss is measured in decibels hearing level (dB HL). If you can hear sounds across a range of frequencies at 0-20dB you are considered as having normal hearing. The thresholds for the different types of hearing loss are as follows:

Mild 20-39dB HL

Moderate 40-69dB HL

Severe 70-90dB HL

Profound 90dB+ HL

What does it mean to have a hearing loss?

You’re not alone

The impact on our lives and those around us from hearing loss can be far-reaching. It becomes harder to distinguish between speech and noise. You can feel lonely or frustrated. You may fall behind at work, limit your social life, and just ‘miss out’. But you are not alone - although aging causes our ears to deteriorate, 20% of all 40 to 60 year olds also have some form of hearing loss. However, a lack of knowledge and social stigma prevent many from being helped by simple, effective solutions.

How people classify themselves relative to hearing loss is a very personal decision and reflects much more than just their ability to hear. It can be difficult too because hearing loss is often not constant. Hearing impaired people with partial loss of hearing may find that the quality of their hearing varies from day to day, or from one situation to another or not at all.

There are many effects of untreated hearing losses which can get worse over time. Many feel anxiety or a lack of confidence. This could cause depression or cause people to withdraw from group or social situations due to a sense of lack of control and intimacy with friends and family. There can also be a negative effect on people’s perceptions of you, which often manifests itself as the idea that you may be somehow less intelligent. Well, that’s the bad news! The good news is that if you are worried about a hearing loss, solutions that will enable improvements are now available.

Introduction to hearing aids

At a basic level a hearing instrument or Hearing aids is an electronic, battery-operated device that amplifies sound. In a digital device, sound is received through a microphone and then converted into electrical signals. A tiny amplifier increases the loudness of the signals, transmitting them back to sound through a speaker into the ear canal. Other signal modifications can also be done within the digital chip to improve the sound quality, particularly of speech sounds.

Types/styles of hearing instruments

In recent years hearing professionals have seen large changes, not just in what hearing devices can do, but how they are worn. These changes can be attributed to a reduction in the size of components, increased durability and cosmetic concerns on the part of the wearer. Four main styles exist and suitability to each type will depend on factors such as degree of hearing loss and physical dexterity.

Behind-the-ear (BTE)

This device is housed in a small, usually curved case behind the ear and the sound is delivered into the ear canal via a custom-made earmould or tubing system. Thin tubings are a relatively recent design change; and are referred to within the industry as ‘open fits’ as they tend to fill less of the outer ear and ear canal than a custom made earmould. The thin tubes usually end is in a soft silicon dome, of varying size. BTE designs have become smaller and smaller over the years, and the introduction of so-called receiver-in-the-canal products have contributed to this development. Receiver-in-the-canal means that the receiver or loudspeaker component sits within the ear canal, and is connected via a thin wiring (usually enclosed in plastic) to the rest of the circuitry which sits in casing behind the ear.

In-the-ear (ITE)

ITEs are completely contained in a casing that fits into the pinna. They are easy to handle, give reasonable easy access to controls and they are sometimes visible when standing face to face with someone.

In-the-canal (ITC)

ITC aids are smaller, filling only the bottom half of the external ear and this makes them more appealing in a cosmetic sense; you cannot usually see very much of this hearing aid when you are face to face with someone.

Completely-in-the-canal (CIC)

Along with ITCs and ITEs, CICs are considered to be more modern and cosmetically appealing CICs fit so deep in the ear canal that they are practically invisible. The ear canals of some individuals might be too small to fit the device into.

Tinnitus

Tinnitus is most commonly referred to as ‘ringing in the ears’, but there are many different types of tinnitus. Tinnitus can vary in terms of the way it sounds (chirping/clicking/pulsing), its severity, as well as its annoyance. Individuals can report intermittent episodes that are not very bothersome, to a constant tinnitus that can negatively influence daily life. It can occur a few times a month or many times in one day; it can occur for a few moments or hours; it can even be constant without relief while sleeping.

Tinnitus is actually heard by most people at some point in their lives, even those with normal hearing. It can be a by product of loud noise exposure, such as after a rock concert. It can also happen spontaneously without any reason, and then disappear as strangely as it began. Many individuals believe this is just a function of the normal hearing system. It is when tinnitus starts to negatively affect one’s life that further consultation may be necessary.

Tinnitus is very real, as it is a ‘sound’ that is heard by the person experiencing it, regardless if someone else can hear it. As tinnitus can be a sign of certain medical complications, it should never be dismissed or underestimated. You should see you’re your GP or hearing healthcare professional as soon as possible should you have persistent tinnitus, or if your tinnitus is accompanied with any dizziness and/or balance problems.